Hello, as the title says, i got 20L of prepared mix with bio-grow, bio-bloom and bio-heaven in it, that has been sitting for 2 days (with an occassional stir) because they didnt need it when i thiught they would. So now my question is, can i still use it? Today it was smelling a bit weird.

I wouldn't.
I don't know about Science, I would go by my nose and by "Rule of Thumb". You say it smells wierd, and the "Rule of Thumb" says use it when freshest. Therefore, I'd be pouring it away.

Ok, thanx for your time, i appreciate it.

ditch it... don't know the truth of the matter but you'll kick yourself if you don't... save yourself the hassle for the sake of a few quids worth of biobizz.